Method of diagnosing component failure in a DC voltage regulator

ABSTRACT

The determination of specific faulty components in an automotive type DC voltage regulator is accomplished by detecting the presence or absence of harmonic frequencies, of the base operating frequency of an associated DC voltage generator, on terminals of the regulator in its operating environment.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to the field of diagnostic methods andmore specifically to the area of diagnosing component failure by sensingthe presence or absence of certain harmonic frequencies at the externalterminal connections of an automotive type DC voltage regulatoroperating in combination with a mechanically driven DC generator.

2. Description of the Prior Art

Solid state type DC voltage regulators are commonly employed inautomotive vehicles to provide voltage level output control forassociated DC voltage generators that are mechanically driven byassociated vehicle engines.

The generators provide both system voltage to the vehicle and chargingcurrent to associated storage batteries.

Conventionally, whenever a component within the regulator fails, thecomplete regulator unit is often replaced. This often occurs since afair amount of electronic troubleshooting skill is necessary in order topinpoint the individual faulty component. While manufacturers may haveequipment and personnel to perform lengthy resistance and voltage checksto diagnose the failed components, service garages and individualvehicle owners more than likely do not.

SUMMARY OF THE INVENTION

The present invention provides a method whereby a technician utilizingeither auxiliary test equipment or onboard sensing devices can monitorthe DC voltage regulator in its working environment and provide a rapiddetermination as to which of several most commonly failing componentsare defective and allow for that single component to be replaced. If theseries of steps within the method determine that none of the mostcommonly failing components are defective, then the entire unit can bereplaced and returned to a rebuilding facility. If, on the other hand, afaulty component is identified, then it is only necessary to replacethat component in the regulator.

The present invention is also intended to be a quick and inexpensivemethod of confirming that the DC voltage regulator has beensatisfactorily built by its manufacturer so as to meet operationalspecifications.

The method of the present invention is used to diagnose componentfailure in DC voltage regulators having terminals connected to amechanically driven generator for sensing its output as well ascontrolling the field current to regulate the generator output. Themethod includes the steps of defining the fundamental frequency, as therotational speed of the associated engine multiplied by the number ofpoles on the rotor of the alternator and the rotational drive ratio;providing means for sensing harmonics of the fundamental frequency;selectively connecting the sensing means to the terminals of the DCvoltage regulator; and comparing the presence or absence of harmonicfrequencies sensed at each terminal with a predetermined fault table todetermine the faulty component in the DC voltage regulator.

By such comparison, a single component within the DC voltage regulatorcan be pinpointed as either being faulty or as having the wrongelectrical characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a typical DC voltageregulator as it is connected to a mechanically driven alternator in abattery charging system for a vehicle.

FIG. 2 is a flow diagram illustrating the method steps of the presentinvention.

FIGS. 3-8 are frequency versus magnitude plots taken at each terminal ofthe voltage regulator indicating normal operation signals and signalsoccurring when the voltage regulator is operating with various defectivecomponents.

FIG. 9 is a block diagram of an electrical apparatus for implementingthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A typical voltage regulator circuit is shown in FIG. 1 connected tooperate in conjunction with a mechanically driven alternator(generator), a DC storage battery and a warning indicator lamp. As inmost vehicular electrical systems, when the battery voltage isswitch-connected to start an associated internal combustion engine (notshown), the charge on the battery is drawn down and, without recharge,would eventually be depleted. When the associated engine is energizedand running, the alternator, which is mechanically driven by the enginethrough a pulley and belt system at a speed multiple of the enginespeed, the alternator is controlled by the regulator to output a voltagehigher than the rated value of the battery to recharge the battery. Thevoltage regulator controls the amount of field current going to therotating field winding of the alternator. The DC voltage potential atthe connection of the rectified output of the alternator and the batteryis compared to a reference level, as determined within the regulator.The field current is controlled according to that comparison.

Specifically, the voltage reference and control circuit of the regulator10 senses the alternator output voltage at the "BAT" connection on its"A" terminal of the regulator. The voltage reference and control circuitis defined by resistors R1, R2, R3, and R4, capacitor C1, zener diode D2and transistor Q2. This circuit acts to modulate the conduction periodfor the output stage Q1 to thereby regulate the current supplied to thealternator field winding. Since the alternator output voltage isdirectly proportional to the speed and average field current, thevoltage reference and control circuit acts as a feedback network bymonitoring the output of the alternator 20 and modulating the fieldcurrent to adjust the output.

The system regulation level is temperature compensated to insure directcharging characteristics for the battery. The temperature compensationis accomplished by means of the temperature coefficients of the zenerdiode D2 reference and the emitter-base junction of the transistor Q2 inthe voltage reference and control circuit. The system voltage variesinversely with the ambient temperature due to those temperaturesensitive elements.

The alternator stator winding potential is half-wave rectified andmonitored by a solid state relay in the regulator which in turn switchesoff a warning indicator lamp I-1 when the rectified value of the statorvoltage accumulates to a predetermined level.

In operation, the closing of an ignition switch S-1 energizes a warninglamp I-1 from the positive terminal of a battery 18 through resistor R8and normally conductively biased transistor Q4. It also turns on theregulation section of the regulator 10 through resistor R10 andtransistor Q3. With Q3 in a conducting state, a calibrated resistor R1and resistor R2 form a voltage divider network. A zener diode D2 iscalibrated by selection to control the maximum voltage level that may bepresent at the base of Q2, which in turn controls the amount of fieldcurrent that will be gated to flow in the Darlington transistor Q1(formed from transistor pair Q1a and Q1b) and the field winding of thealternator 20. While the rotor field winding 22 of the alternator 20 isrotationally driven via the engine and field current is flowing via sliprings 26 and 24 an output voltage is induced in the stator windings 28,30 and 32. As the alternator rotator speed increases from the initialstart-up, its output and the voltage at the stator terminal 34 increasesfrom 0 to the system regulation level determined by the regulator 10.Three phases of AC voltage are generated across the stator windings as aresult of being induced by the rotating field winding on the rotor. Eachphase of AC voltage is fed to rectifier diodes having a common outputconnection on line 48, that is connected to the positive terminal of thebattery 18 for providing charging current thereto as well as vehiclesystem power.

When the stator voltage at point 34 increases to a value ofapproximately 6.5 volts, and the half-wave rectified voltage acrossdiode D3 is accumulated in capacitor C3, the solid state relay circuitdefined by resistor R9, resistor R12, transistors Q5 and Q4, as well asresistors R7 and R8 cause the warming lamp I-1 to be de-energized bychanging the base emitter bias at Q4.

Statistically, it has been found that the most common failures withinthe regulator 10 occur due to transistor Q1a, of the Darlingtontransistor Q1, opening; transistor Q1a, of the Darlington transistor Q1,shorting; transistor Q1b, of the Darlington transistor Q1, shorting;zener diode D2 undercompensating by having a low zener threshhold value;or capacitor C3 becoming open. The present invention is intended toidentify those component failures when a system fault occurs, if in factthat fault is caused by one of those more commonly failing components.

Due to the fact that the rotor of the alternator 20 is driven at aparticular rotational speed by the associated internal combustionengine, the rotational speed of the rotor determines the fundamentalfrequency "f₀ " for the system. The fundamental frequency f₀ becomes afunction of the engine speed and therefore may be determined by thefollowing formula:

    f.sub.0 =(S/60)×r×p

wherein S equals engine speed; r equals drive pulley ratio (2.9 in theexemplified embodiment); p equals number of poles on the rotor of thealternator (six in the exemplified embodiment). Therefore, for an enginespeed of 1,000 rpm, the base frequency f₀ will equal 290 hz. The nthharmonic of f₀ is defined to be n * f₀ and is denoted as fn.

The following table illustrates the frequency signatures of currentmeasurements taken at the four terminals (I, A, S and F) of theregulator 10 under both normal conditions and various fault conditions.

                  TABLE I                                                         ______________________________________                                        Summary of Regulator Defects                                                  & Their Distinguishing Frequency Signatures                                                   Frequency at which                                            Regulator       Distinguishing Spikes Occur                                   Defect Characteristic                                                                         Term I  Term A   Term S                                                                              Term F                                 ______________________________________                                        Normal          None    Multiple f.sub.3                                                                             f.sub.6                                Q1a open - light on -                                                                         None    None     None  None                                   no field current                                                              Q1a shorted - full charge                                                                     None    Multiple f.sub.3                                                                             None                                   D2 under-calibrated -                                                                         None    Multiple None  f.sub.6                                under charge                                                                  C.sub.3 open - light on                                                                       f.sub.3,f.sub.6                                                                       Multiple f.sub.3                                                                             f.sub.6                                Q1b shorted - random                                                                          None    f.sub.6  f.sub.3                                                                             f.sub.6                                charging                                                                      ______________________________________                                    

Applicants observed that every fault resulted in a change of theexistence of different harmonics measured at the four terminals ofregulator 10, thus providing a viable diagnostic method. That method isillustrated in FIG. 2 as a flow diagram in which the steps of the methodare illustrated.

Initially, terminal S of the regulator 10 is monitored to determine ifthe third harmonic f₃ is present. If the third harmonic f₃ is notpresent on the S terminal, the F terminal is monitored to determine ifthe sixth harmonic f₆ is present thereon. If the sixth harmonic is notpresent on the monitored F terminal, a determination is made that Q1a isopen. In the event the sixth harmonic is sensed on the monitored Fterminal, it is determined that zener diode D₂ is under-calibrated.

If, on the other hand, the third harmonic f₃ is sensed on the Sterminal, the F terminal is monitored to determine if the sixth harmonicf₆ is present thereon. If the sixth harmonic is not present, it isdetermined that Q1a is shorted.

If, the third harmonic f₃ is sensed on the S terminal and the sixthharmonic is sensed on the F terminal, the A terminal is then monitoredto determine if the sixth harmonic is present thereon. If the sixthharmonic is present on the A terminal at an amplitude greater than apredetermined value, it is determined that Q1b is shorted.

If, however, the sixth harmonic is not sensed at the terminal A to begreater than the predetermined amplitude, terminal I is then monitoredto determine if both the third and sixth harmonics are present thereon.If both harmonics are sensed as being present on terminal I, adetermination is made that C3 is open. If, on the other hand, the thirdand sixth harmonics are not sensed as being present on terminal I, thesystem will not produce an identification of a specific defect.

FIGS. 3-8 contain plots of amplitude values of various frequenciespresent on designated terminals of the alternator. FIGS. 3, 4, and 5illustrate the affects of the component Q1a being open and resulting ina symptom of the alternator not charging the battery. The FIGS. 3, 4 and5 compare the defect with the normal measurements taken at terminals A,S and F, respectively.

FIG. 6 illustrates the frequencies measured at terminal A when thecomponent Q1b is shorted, as compared to normal frequency measurementsmeasured at that terminal.

FIG. 7 plots the frequency measurements taken at terminal S at both thenormal condition when the third harmonic is present and under the defectcondition when no harmonics are present because diode D2 isunder-calibrated.

FIG. 8 is a plot of the frequency measurements taken at terminal I undernormal conditions when no harmonics are detected and under defectconditions when component C3 is open, causing the third and sixthharmonics to be measured.

FIG. 9 is a block diagram illustrating an electronic circuit used forperforming the above described diagnostic method. A sampling gate 220 isconnected to each of the four terminals (I, A, S and F) of the voltageregulator and is commanded to gate the signals on those terminals to atracking filter 240 by an appropriately programmed microprocessor 50.The tracking filter 240 is configured to pass the third and sixthharmonics as determined by the base input frequency f₀, which is derivedaccording to the engine speed. Microprocessor 50 is programmed toconvert engine speed to the base frequency that controls the trackingfilter 240; to sequentially provide sampling control signals to thesample gate 220; and to process the output of the tracking filter 240 ina sequence of steps similar to those shown in FIG. 2 to provide a faultidentification that is output to a display device (not shown).

It will be apparent that many modifications and variations may beimplemented without departing from the scope and novel concept of thisivention. Therefore, it is intended by the appended claims to cover allsuch modifications and variations which fall within the true spirit andscope of the invention.

We claim:
 1. A method of diagnosing component failure in a DC voltageregulator means having terminals connected to sense the voltage leveloutput from and control the field current supplied to an associatedmechanically driven DC voltage generator means including the stepsof:defining a fundamental frequency as the frequency of rotation of themechanically driven rotor field winding of the generator meansmultiplied by the number of poles on the rotor; providing means forsensing predetermined harmonics of said fundamental frequency;selectively connecting said sensing means to terminals of said regulatormeans; and comparing the presence or absence of harmonic frequenciessensed at each terminal with a predetermined fault table to determinethe specific faulty component in said DC voltage regulator.
 2. A methodas in claim 1 wherein said rotor is of the six pole variety having threestator windings and said step of comparing specifically senses thepresence or absence of at least the third and sixth harmonic frequenciesand includes the step of distinguishing therebetween.
 3. A method as inclaim 2 wherein said DC voltage regulator includes a first terminalconnected to the rectified output of said generator means and to aterminal of a means for storing DC energy, a second terminal connectedto a common junction of the stator windings of said generator means anda third terminal connected in series with the field winding of saidgenerator means;a power transistor for supplying field current from saidfirst terminal to said third terminal; a voltage sensing circuitincluding a reference diode for turning on said power transistor whenthe voltage level at said first terminal is below a value determined bythe threshhold level of said reference diode; and wherein the failure ofeither said power transistor of said reference diode is determined bysaid method.
 4. A method as in claim 3, wherein the occurrence of saidpower transistor being open, so as to prevent field current from beingsupplied to said field winding of said generator means, is detected bythe absence of said harmonic frequencies being sensed at any of saidsecond and third terminals.
 5. A method as in claim 3, wherein theoccurrence of said power transistor being shorted, so as to supplyunregulated full current to said field winding of said generator means,is detected by sensing the presence of only said third harmonicfrequency at said second terminal and the absence of said harmonicfrequencies at said third terminal.
 6. A method as in claim 3, whereinthe occurrence of said reference diode having a low threshhold referencevalue, so as to prevent an appropriate flow of field current throughsaid power transistor to said third terminal, is detected by sensing theabsence of said harmonic frequencies at said second terminal and thepresence of only said sixth harmonic frequency at the third terminal. 7.A method as in claim 3, wherein the occurrence of said power transistorbeing partially shorted, so as to supply randomly regulated current tosaid field winding of said generator means, is detected by sensing thepresence of a high magnitude of said sixth harmonic frequency at saidfirst terminal.
 8. A method as in claim 3, wherein said DC voltageregulator further includes a fourth terminal connected to one side of afilament indicator lamp and to a normally closed voltage sensitive relaythat is connected to said second terminal to sense the stator windingvoltages of said generator means, wherein said voltage sensitive relayincludes a rectifying diode having its anode connected to said secondterminal and a storage capacitor connected between the cathode of saiddiode and ground to store the rectified stator voltage from said diodeand provide a holding voltage for said relay when said holding voltageexceeds a predetermined value, wherein the occurrence of said storagecapacitor being open and allowing said voltage sensitive relay to remainin its closed state is detected by sensing the presence of only saidthird harmonic frequency at said second terminal, the presence of onlysaid sixth harmonic frequency at said third terminal and the presence ofboth said third and sixth harmonic frequencies at said fourth terminal.9. A method as in claim 8, wherein the occurrence of said powertransistor being open, so as to prevent field current from beingsupplied to said field winding of said generator means, is detected bythe absence of said harmonic frequencies being sensed at any of saidfirst, second and third terminals.
 10. A method as in claim 8, whereinthe occurrence of said power transistor being shorted, so as to supplyunregulated full current to said field winding of said generator means,is detected by sensing the presence of only said third harmonicfrequency at said second terminal and the absence of said harmonicfrequencies at said third terminal.
 11. A method as in claim 8, whereinthe occurrence of said reference diode having a low threshhold referencevalue, so as to prevent an appropriate flow of field current throughsaid power transistor to said third terminal, is detected by sensing theabsence of said harmonic frequencies at said second terminal and thepresence of only said sixth harmonic frequency at said third terminal.12. A method as in claim 8, wherein the occurrence of said powertransistor being partially shorted, so a to supply a randomly regulatedcurrent to said field winding of said generator means, is detected bysensing the presence of a high magnitude of said sixth harmonicfrequency at said first terminal.